I had a GM who handed us a homebrew campaign (setting, classes, the whole shebang) where I played the main caster type. He didn't follow the nat 20 means auto success roll rule on anything except attack rolls, so naturally this meant that when he decided to toss a dragon at us with spell resist literally higher than anything I could ever roll (something he had given it, not what normal rules gave it) I tried calling bullshit since I was forced to use a quarterstaff I kept around just for back up.

I don't know... see, as a GM myself, if I was doing that, it would be because I'd have something else in mind for that dragon other than it being defeated immediately in combat, and I'd make it abundantly clear that the party was not capable of fighting it under normal circumstances, provide obvious escape routes or make the dragon act in a strange way that would hint towards a better way of beating it. Making a particular encounter impossible to complete by the usual methods of the party isn't a bad thing... that said, if it was just a matter of you swinging away with a quarterstaff while the fighters did all of the work, then something's gone wrong unless the DM had some sort of story thing in mind or unless spells in this homebrew setting were totally broken unless there were some monsters running around with insane spell resistance.